Electrostatic process for reproducing an image formed by discontinuous raised areas

ABSTRACT

AN ELECTROSTATIC PROCESS COMPRISES REPRODUCING A VISIBLE IMAGE FORMED BY DISCONTINUOUS AREAS ON A SURFACE OF AN OBJECT AS A LATENT ELECTROSTATIC IMAGE ON A SURFACE OF A DIELECTRIC MATERIAL. THE SURFACE OF THE OBJECT IS POSITIONED IN CONTACT WITH A SHEET OF DIELECTRIC MATERIAL WHICH, IN TURN, IS PLACED IN CONTACT WITH AN ELECTRODE. A SOURCE OF POTENTIAL IS APPLIED ACROSS THE OBJECT AND THE ELECTRODE THEREBY CREATING AN ELECTRIC FIELD. THE SOURCE OF POTENTIAL IS REMOVED PRIOR TO ITS BEING DE-ENERGIZED AND THE DIELECTRIC MATERIAL IS THEN REMOVED WHEREBY AN ELECTROSTATIC CHARGE PATTERN CORRESPONDING TO SAID AREAS IS PRODUCED ON THE SURFACE OF SAID DIELECTRIC MATERIAL AND DEVELOPED XEROGRAPHICALLY TO PRODUCE A VISIBLE IMAGE.

June 15, 1971 H. B. ALLINGER ETAL BY DISCONTINUOUS RAISED AREAS Filed July 29, 1968 Fry.

/4 Electrode l3 Power Dielectric Mater/P j ,2 Supp/y L l\ Object i0 (Electrically 1 Conductive) /5 Fly. 2

E lectro de 0 23 7 24 Dielectric Material-W 22 PP y Object Nan-Conductive) 26 Electrode &

Fly. 3 Electrode Q l Dielectric Plote)/' I I 1 "A33 (Glass) l 3 Dielectric Material 2 Power Object 7h PP/y (Alon Conductive) Dielectric Plate (Gloss) I [M fi-36 Electrode 3/ 5 5 I L SUPPLY 1p} BY 4 f HUBERT B. ALL/NGER THEODORE H MORSE INVENTORS AGE/VT United States Patent O M 3 585,061 ELECTROSTATIC PROCESS FOR REPRODUCING AN IMAGE FORMED BY DISCONTINUOUS RAISED AREAS Hubert B. Allinger and Theodore H. Morse, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester N.Y.

, Filed July 29, 1968, Ser. No. 748,560

Int. Cl. G03g 13/04, 13/08, 13/10 US. Cl. 11717.5 6 Claims ABSTRACT OF THE DISCLOSURE An electrostatic process comprises reproducing a visible image formed by discontinuous areas on a surface of an object as a latent electrostatic image on a surface of a dielectric material. The surface of the object is positioned in contact with a sheet of dielectric material which, in turn, is placed in contact with an electrode. A source of potential is applied across the object and the electrode thereby creating an electric field. The source of potential is removed prior to its being de-energized and the dielectric material is then removed whereby an electrostatic charge pattern corresponding to said areas is produced on the surface of said dielectric material and developed xerographically to produce a visible image.

STATEMENT OF THE INVENTION The present invention relates to electrostatic copying of an image-bearing object and, more particularly, to an electrostatic process for reproducing an image formed by discontinuous areas on the surface of the object as a latent electrostatic image on a surface of a dielectric material which can subsequently be developed into visible image.

DESCRIPTION OF THE PRIOR ART Electrophotography includes xerography which utilizes electrostatic images in the form of surface charge patterns. It is possible to form an electrostatic charge image on a dielectric film while such film is in contact with a photoconductive surface. By this process, a high voltage is applied across the dielectric film and the photoconductor material to produce an electric field in the areas Where the photoconductor is exposed to light with electrical charges transferring to the dielectric film from the photoconductive layer in the exposed areas. However, before the photoconductive layer can be exposed to light, it is necessary to uniformly charge the surface of the photoconductive material.

The processes by which charge transfer to a dielectric material is accomplished are often referred to as TESI processes (Transfer of Electrostatic Images). In each of these processes a xerographic plate is used in conjunction with a dielectric material as the image receiving member. However, the xerographic plate must be either uniformly charged and imagewise exposed before being placed in contact with the dielectric material, or uniformly charged and then imagewise exposed after being placed in contact with the dielectric material. The certain of these processes the dielectric material is also uniformly charged before or after it is placed in contact with the xerographic plate. As a result, the TESI processes are capable of providing a charge transfer only between a xerographic plate and a dielectric material.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide an electrostatic process for reproducing an image formed by discontinuous areas on the surface of an electrically conductive object as a latent electrostatic image on the surface of a dielectric material.

Another object of the invention is to provide an electrostatic process for reproducing a visible image formed by discontinuous areas on the surface of an electrically conductive object in which an electrostatic latent image is formed on a surface of a dielectric material as an electrostatic charge pattern corresponding to the areas, the charge pattern being capable of being developed xerographically to produce a visible image.

Still another object of the invention is to provide an electrostatic process for reproducing a visible image formed by discontinuous areas on the surface of an electrically conductive object in which an electric field is established across the object and a dielectric material in contact with the areas for producing an electrostatic charge pattern corresponding to the areas in contact with the surface of the dielectric material.

These and other objects of the invention will be apparent to those skilled in the art by the detailed description of the invention which follows:

The objects of the invention are attained by an electrostatic process in which a sheet of dielectric material having one surface in contact with an electrically conductive member is positioned with the other surface thereof in virtual contact with the image surface of an electrically conductive object. A source of potential is then applied to the object and the conductive member to established an electric field thereacross. Under the influence of the electric field, unbound charges migrate to produce an electrostatic image. The source of potential is then disconnected from the object and conductive member before it is de-energized. The dielectric material is then removed from the object and on separation ionization occurs, as a critical gap spacing-potential relationship is reached. This ionization enhances the charge image on the surface of the dielectric material so that in the regions of the discontinuous areas a charged electrostatic image is formed on the surface of the dielectric material which is a reverse reading copy of the object image. The electrostatic image can then be developed xerographically by a dry, electrostatic toner or the dielectric material can be immersed in an insulating liquid in which toner par ticles are dispersed. By utilizing a tonner which permits transfer of the image from the dielectric material to another receiver sheet a right-reading copy can be made.

The term electrically conductive object is used herein above, throughout the more detailed description of the invention which follows, and in the appended claims to denote an electrically conductive metal foil having an embossed image thereon that can be formed into or raised from the foil surface; for example, a letter press or Grave ure-type printing plate; or the combination of an insulating material and an electrically conductive backing member. The latter can be either in contact with or an integral part of the insulating material, for example, paper having an embossed image on one surface that is formed into or raised from said one surface and the other surface coated with a metallic electrically conductive material, or with the other surface in contact with an electrically conductive member, such as a metallic plate. Also, the term dielectric material is meant to include paper having a dielectric coating on at least one surface thereof, such as a coating of polystyrene, polyethylene, polytetrafluoroethylene, etc., or a sheet per se of any of the previously-mentioned plastic coating materials. In other words, dielectric material is meant to include any material that is capable of retaining an electrostatic charge for a sufficient length of time to enable the latent electrostatic image produced thereon to be developed into a visible image or to permit the developed image to be transferred to another receiver sheet. The electrically conductive member in contact with the dielectric material can be in actual contact with, or an integral physical part of, the dielectric material. In the latter case, an electrically conductive material can be coated on one surface of the dielectric material; for example, a sheet of paper can be coated on one surface with a dielectric material and on the other surface with an electrically conductive material, or the electrically conductive material can be in the form of a sheet that is bonded to the other surface of the dielectric material.

DESCRIPTION OF II-IE DRAWING Reference is now made to the accompanying drawing wherein like reference numerals designate like parts and wherein:

FIG. 1 is a schematic sectional view of one embodiment of the invention in which the object is electrically conductive and showing the relationship of the dielectric material, the object and the manner in which the power supply is connected thereto;

FIG. 2 is a schematic sectional view of another embodiment of the invention similar to that shown in FIG. 1 and showing the object as a nonconductive member having an electrically conductive member in contact therewith;

FIG. 3 is a schematic sectional view of another embodiment of the invention similar to that shown in FIG. 2 in which dielectric plates are interposed in the structure to control the intensity of the electric field; and

FIG. 4 is a schematic view similar to FIG. 1 and shows the charge distribution for the electric field established by a source of potential applied to the object and an electrode in contact with one surface of the dielectric material arranged therebetween.

DESCRIPTION OF THE INVENTION With reference to FIG. 1, an object is disclosed as a conductive member having raised portions 11 which form a visual image on the surface of the object. Such an object can be a metal stencil, an addressographic plate, a letter press or Gravure-type printing plate, etc. In order to reproduce an image of this surface electrostatically, a

dielectric material 12 can be positioned in contact with s the raised portions 11 and an electrode 13 then placed in contact with the dielectri material. By connecting a high voltage power supply 14 between the electrode 13 and the object 10, an electric field is established between the object 10 and the electrode 13. Due to this electric field, unbound charges migrate to the interface of the dielectric material at the areas of contact to establish a charge pattern on the surface of the dielectric material that corresponds to the raised portions 11. The power supply 14 is then disconnected from the electrode and the object before it is de-energized to prevent the charge pattern from leaking ofl? to ground and, hence, from being erased from the dielectric material. Such disconnection can be accomplished by a switch 16 as shown in FIG. 4. Once the power supply has been removed, the electrode 13 and the dielectric material 12 are removed from object 10 and, upon such separation, an electrostatic image is formed on surface 15 of dielectric material 12. Dielectric material 12 is then removed from electrode 13 and the electrostatic image is developed by known xerographic development methods, such as application of a dry toner to surface 15 or immersion of the dielectric material 12 in an insulating liquid containing toner particles dispersed therein.

The high voltage power supply 14 is maintained for an interval that is sufficient to generate the necessary electric field and then de-energized. It has been found that such interval can vary from less than one second to about 10 seconds. A voltage level from about 300-15,000 volts can be used depending on the conductivity of the object whose surface is being copied. As mentioned above, in this embodiment of th invention the Object i electrically conductive and there is no need for a conductive backing member so that the power supply can be connected directly to the object 10. A positive or a negative latent electro static image can be produced on the surface 15 in accordance with the polarity connection that is made to the object 10 and to electrode 13. Assuming that the polarity of the toner is not changed, a positive or a negative image can be produced depending on the polarity connections.

With reference to FIG. 4, the unbound or free charges derived from the power supply 14 position themselves substantially as shown. Higher charge densities occur in the image areas, that is, in those areas where the raised portions 11 are in contact with the surface 115 of the dielectric material 12, due to the higher capacitance in these areas. As a result, higher electric field intensities exist in the image areas as compared to the areas that might be considered as the background areas. In the minute air gap that necessarily exists between the surfaces in contact, the higher electric field strength in the adjoining areas is believed to be sufficient to cause ionization of the air so that positive charges deposit on the surface of the dielectric material in the image areas. When the power supply 14 is disconnected by opening switch 16, the assembly of sheets is then separated. With separation of the dielectric mate rial 12 and the electrode 13 from the object 10, ionization again occur as a critical gap spacing-potential relationship is reached between the surface 15 of the dielectric material and the raised portions 11 of the object. This ionization enhances the charge image on the surface 15 and by disconnecting the power supply 14 before the separation is accomplished, it is believed that the charges trapped on the electrode 13 aid the ionization that takes place with the initial separation.

In FIG. 2 the relation of the various elements is substantially the same as that shown in FIG. '1. However, in FIG. 2 an object 20 is disclosed as being generally electrically nonconductive so that in this case the object must be positioned in contact with an electrode 26 to which one side of a power supply 24 is connected. As in FIG. 1, a surface 25 of a dielectric material 22 is placed in contact with the raised portions 21 of the object and the other surface of the dielectric material is then contacted with an electrode 23. The same steps as described above with respect to FIG. 1 are followed in the arrangement shown in FIG. 2 to produce an elecrostatic imge on surface 25. -In this disclosure object 20 can be a sheet of paper having embossin-gs thereon which are represented by the raised portions 21. Also, object 20 can be a stencil or matrix in which the raised portions 21 are obtianed by removing areas from the surface of the object by a mechanical or process whereby the raised portions 21 constitute a visible image.

In FIG. 3 an embodiment of the invention is shown which is similar to that shown in FIG. 2. However, in instances where an available power supply 34 is not compatible with the copying process, that is, the minimum voltage is such that the intensity of the electric field is too great, glass plates 37, 38 can be used to reduce the intensity of the electric field. In this case, glass plate 38 is interposed between dielectric material 32 and electrode 33 and glass plate 3 7 is interposed between the object 30 and electrode 36. The thickness of plates 37, 38 will vary in accordance with the necessary reduction that must be made in the field intensity.

The manner in which the latent electrostatic image is formed on surfaces 25 and 35 in the embodiments disclosed in FIGS. 2 and 3 is substantially the same as in FIG. 1 and as more fully described with respect to FIG. 4. In FIG. 2 the electric field is between the electrodes 23 and 26, whereas in FIG. 3 the strength of the electric field bewteen electrodes 33 and 36 is reduced due to the interposition of plates 37 and 38.

With the process described above it has been found that copies can be made of objects whose surfaces contact the dielectric material in relatively small separated areas as well as those which contact the dielectric material.

in relatively large areas. Due to the difficulty in achieving good physicl contact and uniform charge transfer between the discontinuous areas and the dielectric material, it is preferable that the discontinuous areas be relatively small area-wise. On the other hand, surface protrusions of at least 0.00025 can be detected and a resolution of at least 100 lines per inch is possible with the process of the invention. In addition to the various objects described above that can be copied, it has been found that areas of different conductivity on a planar surface can also be copied; for example, a printed circuit in which the circuit is embedded in an insulating material and coplanar with the surface of the insulating material. A copy of such a circuit can be made by the process described herein. Also, a copy of a printed circuit in which the circuit is carried above or below the plane of the insulating carrier plate can be made by this process. Accordingly, the process is capable of making a copy of an image configuration on an object in which the discontiuous areas defining the image are coplanar with a plane of the object or displaced above or below such plane.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim: 1. An electrostatic process for reproducing a visible image formed by electrically nonconductive discontinuous raised areas on one surface of an electrically nonconductive object as a latent electrostatic image on one surface of a dielectric material, comprising the steps of interposing said object and dielectric material with said one surface in contact with said raised areas between and in contact with the facing surfaces of a pair of spaced dielectric plates,- each of which has an electrode in contact with the other surface thereof;

applying an electrical potential across said electrodes for generating an electrical field therebetween, the intensity of which is controlled by said dielectric plates, whereby an electrostatic charge pattern is produced on said one surface in accordance with said raised areas;

disconnecting said electrical potential from said electrodes, while maintaining the stacked relation-of said electrodes, dielectric plates, dielectric material and object;

removing said electrodes and dielectric plates from said stacked relationship; and

stripping said dielectric material from said object in successive portions, whereby ionization occurring in the gap between said dielectric material and said raised areas will enhance said electrostatic charge pattern on said one surface.

2. The electrostatic process in accordance with claim 1 including the step of developing said electrostatic charge pattern on said dielectric material to produce a visible image.

3. The electrostatic process in accordance with claim 1 wherein said dielectric plates are glass.

4. The electrostatic process in accordance with claim 1 wherein said dielectric material is paper having an electrically insulating material coated on at least one surface thereof.

5. The electrostatic process in accordance with claim 4 wherein said electrically insulating material is polytetrafluorethylene.

6. The electrostatic process in accordance with claim 4 wherein said electrically insulating material is polyethylene.

References Cited UNITED STATES PATENTS 2,647,464 8/1953 Ebert 117--17.5X 2,912,586 11/1959 Gundlach 1l717.5X 2,953,470 9/1960 Green et al. 1l717.5 3,023,731 3/1962 Schwertz 118637X 3,045,587 7/1962 Schwertz 117-17.5X 3,075,859 1/1963 Relph et al. 11717.5X 3,145,655 8/1964 Hope et al. 11717.5X 3,244,546 4/1966 Cranch 11717.5 3,326,709 6/1967 Nail 11717.5 3,408,217 10/1968 Obuchi 11717.5X 3,414,723 12/1968 Pleitt et al. 25049.5 3,441,939 4/1969 Anderson 25049.5X 3,443,517 5/ 1969 Gundlach 101219 OTHER REFERENCES Moradzadeh, Y, and R. M. Schaifert: Nonoptical Electrostatic Reproduction, IBM Technical Disclosure Bulletin, Vol. 8, No. 4, September 1965, pp. 491-2.

WILLIAM D. MARTIN, Primary Examiner E. J. CABIC, Assistant Examiner U.S. Cl. X.R.

101-426, Dig. 13; 118-637; 346--74ES 

